U-Th age evidence from carbonate veins for episodic crustal deformation of Central Anatolian Volcanic Province

Quaternary Science Reviews 177 (2017) 158e172

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U-Th age evidence from carbonate veins for episodic crustal deformation of Central Anatolian Volcanic Province c _ Volkan Karabacak a, *, I. Tonguç Uysal b, Ezgi Ünal-Imer , Halim Mutlu d, Jian-xin Zhao e a

Department of Geological Engineering, Eskisehir Osmangazi University, Turkey The Commonwealth Scientific and Industrial Research Organization (CSIRO) Energy, Perth, WA 6151, Australia c Department of Geological Engineering, Hacettepe University, Turkey d Department of Geological Engineering, Ankara University, Turkey e Radiogenic Isotope Facility, School of Earth Sciences, The University of Queensland, Brisbane, QLD 4072, Australia b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 9 June 2017 Received in revised form 1 October 2017 Accepted 17 October 2017

Central Anatolia represents one of the most outstanding examples of intraplate deformation related to both continental collision and back-arc extension generating non-uniformly distributed stress fields. In this study, we provide direct field evidence of various stress directions and investigate carbonate-filled fracture systems in the Central Anatolian Volcanic Province using U/Th geochronology and isotope geochemistry for evaluating the episodes of latest volcanic activity under regional stress. Field data reveal two independent fracture systems in the region. Successive fracture development has been  Composite Volcano and Acıgo € l Caldera). controlled by two different volcanic eruption centers (Hasandag Trace element, and stable (C and O) and radiogenic (Sr) isotope compositions of carbonate veins indicate different fluid migration pathways for two different fracture systems. The U/Th age data for carbonate veins of two independent fracture systems indicate that the crustal deformation intensified during 7 episodic periods in the last 150 ka. The NNE-trending first fracture system was formed as a result of strain cycles in a period from 149 ± 2.5, through 91 ± 1.5 to 83 ± 2.5 ka BP. Subsequent deformation events represented by the ENE-trending second fracture zone have been triggered during the period of 53 ± 3.5, 44 ± 0.6 and 34 ± 1 ka BP before the first fracture zone resumed the activity at about 4.7 ± 0.15 ka BP. Although further studies are needed to evaluate statistical significance of age correlations, the periods of carbonate precipitation inferred from U-Th age distributions in this study are comparable with the previous dating results of surrounding volcanic eruption events. © 2017 Elsevier Ltd. All rights reserved.

1. Introduction The Eastern Mediterranean region represents one of the most seismically active and deforming parts of the Alpine-Himalayan orogenic belt, with a complex geodynamic evolution resulting from interaction between Eurasian, Arabian, and African plates. The deformation related to the convergence between the Afro-Arabian and Eurasian plates toward north gives rise to widespread and intense arc volcanism in Central and Eastern Anatolia (Innocenti et al., 1975; Aydar et al., 1994, 1995; Piper et al., 2002). Central Anatolia, thus, represents one of the most outstanding examples of intraplate deformation related to continental collision (Fig. 1a). It is

* Corresponding author. E-mail address: [email protected] (V. Karabacak). https://doi.org/10.1016/j.quascirev.2017.10.022 0277-3791/© 2017 Elsevier Ltd. All rights reserved.

widely accepted that recent internal deformation of the Anatolian microplate has been taking place after the continental collision along the Bitlis-Zagros Suture Zone since the late Miocene €r et al. (1985) (Innocenti et al., 1975; Pasquare et al., 1988). S¸engo proposed a relatively lower activity state in the foreground to define the tectonic regime of Central Anatolia, which is affected by a moderate NE-SW compression. However, it has also been suggested that Aegean crustal tectonics dominated by N-S extension and related to the southward rollback of the African subduction under the Aegean and western Anatolia is another mechanism leading to a significant deformation in the Anatolian Block (Reilinger et al., 2006). Dhont et al. (1998) argued that the regional crustal deformation in Central Anatolia is not related to a compressional event, but dominated rather by extensional tectonics. Recent GPS measurements indeed indicate that the deformation affecting Central  et al., 2013; Simao et al., 2016). Anatolia is not uniform (Aktug

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Fig. 1. (a) Generalized geodynamic map of Turkey, (yellow arrows show plate motions and yellow dashed line shows the boundary of the western Anatolian extensional region) (b) shaded relief map of Central Anatolia in the vicinity of the study area (generated using the AsterGDEMv2 digital data). White lines show the active faults (Emre et al., 2011); yellow  et al., 2013; Simao et al., 2016); blue arrows show GPS horizontal velocities (Eurasia fixed) (Aktug  et al., 2013); The reddish area arrows show the principle strain directions (Aktug indicate volcanics of CAVP. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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Direct field evidence of various stress directions in Central Anatolia and the timing of the deformation events are therefore critical for the understanding of crustal evolution and plate interaction in the eastern Mediterranean region. Within intra-plate environments with margins controlled by continental collision, like Central Anatolia, the accumulated strain on upper crust is unloaded with cracks of different scales. Under suitable conditions, extrusion of magma associated with main collisional events may rise through the deep-penetrated cracks and/or their intersection area (e.g. Payenia volcanic province in the Southern Andes (Ramos and Folguera, 2011), High Lava Plains in Oregon (Jordan et al., 2004)). In areas of relatively slower deformation, widespread volcanoclastic products conceal main structures partially or even entirely. During continuing crustal strain cycles, however, new fracture formation may be an ongoing process. Such brittle deformation within volcanic environments is generated by magmato-tectonic stresses in two ways: (1) ascending of extrusive magma (Azzaro, 1999; Zobin, 2003) and (2) magma migration in the crust (Rubin and Gillard, 1998; Rubin, 1992; Gudmundsson, 2003; Gudmundsson and Loetveit, 2005; Doubre et al., 2007; Medynski et al., 2015; Dumuont et al., 2017). Brittle deformation caused by magma movement in the volcanic regions would be expected to occur along the boundary of the magmatic system where shear stress is at maxima and temperatures are low enough for brittle fracture to occur (Rubin and Gillard, 1998; Azzaro, 1999; Glen and Ponce, 2002; Zobin, 2003). The locations of the volcanic seismicity also occur in regions of partial melting (Ogawa et al., 2014; Hill et al., 2009; Ingham et al., 2009). Deformation may be caused by shear failure, tensile failure or fluid pressurization processes that produce the ruptures at the tip of magma body (Rubin and Gillard, 1998; Azzaro, 1999; Glen and Ponce, 2002; Zobin, 2003). Moreover, magma degassing may trigger fracture development in the caldera regions (e.g., Phlegrean Fields (Chiodini et al., 2003) and Colli Albani (Tuccimei et al., 2006)). CO2-bearing spring waters under high pressure in subsurface reservoirs are mobilized during crustal strain cycles whereby carbonates are precipitated in the fractures that act as conduit for hot waters around volcanic eruptions (e.g., Mt. Etna (Alessandro et al., 2007), Semproniano-Southern Tuscany (Berardi et al., 2016)). Investigation of fracture systems and carbonate veins within intraplate volcanic environments is thus important for evaluating recent mechanism of crustal deformation and volcanic activity in areas under regional stress. In the Central Anatolian Volcanic Province (CAVP), there are well-developed fracture systems and associated carbonate vein depositions on widespread volcanoclastic products of the young volcanic activities. Different layers of voluminous volcanic products (e.g., ignimbrites, lavas) originating from numerous Quaternary polygenetic volcanoes and monogenetic cones cover the region (Fig. 1b). Although the most of volcanic eruptions are well studied in terms of morphological, petrographical and geochemical characteristics (e.g., Pasquare, 1968; Innocenti et al., 1975; Batum, 1978; Pasquare et al., 1988; Ercan et al., 1990, 1992; Aydar et al., 1994; Le Pennec et al., 1994; Druitt et al., 1995; Dhont et al., 1998; Toprak, 1998), there is a lack of studies focusing on eruptive history of the region. Dating of volcanism reported by previous studies has been a major challenge because of difficulty in distinguishing the field relationships of volcanic products in spatial and temporal patterns. For example, in volcanic successions, heating of old rocks in contact with relatively younger lavas or hot pyroclastic deposits could partly or completely reset (U-Th)/He zircon ages (e.g., Blondes et al., 2007; Schmitt et al., 2011), rendering the identification of stratigraphic sequences of extrusive materials difficult. Commonly, there are also unrecorded and unpreserved volcanoclastic layers due to depositional and erosional processes (e.g.,

lu et al., 1998). However, without any volcanic eruption, Kuzucuog fluid pressurization related to subsurface magma migration may also generate crustal deformation (Azzaro, 1999; Zobin, 2003; Doubre and Peltzer, 2007). Depressurized fluids migrating to the surface or near surface can be responsible for the deposition of fracture-filling hydrothermal minerals. Investigation of such minerals can provide useful information on the history of regional magmato-tectonic deformation. In the current study, we focused on fracture systems around the Ihlara Valley (Cappadocia) surrounded by well-known volcanic centers with latest activities of the southern CAVP. Such crustal deformation controlled by volcanism is dated for the first time in the literature with a sampling other than extrusive material. We used the U-series dating technique on carbonate veins along fracture systems that allows us to define the late Quaternary and historical records of CO2 mobilization (in the time range of 0e500 ka BP) and related crustal strain cycles in the southern CAVP. Similarly, carbonate veins in seismically active zones have been dated precisely by U-series method to provide important record of fault movements in western Anatolian extensional province and _ Australian intraplate setting (Uysal et al., 2009, 2011; Ünal-Imer et al., 2016; Ring et al., 2016). In addition, trace element, and stable (C and O) and radiogenic (Sr) isotope compositions of fissure carbonate veins are discussed with a special emphasis on fluid sources. 2. Recent deformation of Central Anatolian Volcanic Province As commonly expected along the convergent plate margins, an intense and widespread volcanic activity was initiated in Central Anatolia during the Neogene and Quaternary (Innocenti et al., 1975; Aydar et al., 1994, 1995; Piper et al., 2002). This volcanism has been considered as one of the most outstanding examples of arc volcanism related to the compression (Pearce et al., 1990; Yılmaz, 1990), although it has also been attributed to regional extension (Dhont et al., 1998; Temel et al., 1998). Long-term changes from calcalkaline to alkaline volcanism in the CAVP reflects a gradual transition from flux melting (subduction-related) to decompression melting (extension related) (Aydar et al., 2012; Reid et al., 2017). Despite an ongoing debate on the type and direction of the dominant stress, there is a consensus on volcanic eruption centers of the CAVP showing a distribution parallel to the NE-SW trend of CAVP lu-Kus¸cu et al., 2007). In (Dhont et al., 1998; Toprak, 1998; Gençaliog addition, recent GPS measurements show that deformation in Central Anatolia is not uniform and that a regional dilatation  et al., dominates despite variations in stress directions (e.g., Aktug 2013; Simao et al., 2016). Specifically, a tension stress striking about NW-SE is evident in the study area. The recent morphology of the CAVP has been shaped by NW-SE€ lü Fault Zone (TFZ) in west since Miocene (Dirik and trending Tuzgo € ncüog lu, 1996). The TFZ consists of active normal faults with Go right lateral strike-slip component of about 200 km (Emre et al., , Keçiboyduran, and Melendiz composite 2011). Hasandag volcanos have been developed along the intersections of the TFZ with other smaller scale faults (Pasquare et al., 1988; Toprak and € ncüog lu, 1993a). Go €l Caldera Lineaments are apparent between the TFZ and Acıgo region. Toprak (1998) and Dhont et al. (1998) investigated the volcanic vent distributions in relation to the lineaments. Accordingly, eruption centers and faults are aligned in N-S generally in the central part of the CAVP. These alignments tend to be gradually parallel to TFZ around the study area. The Ihlara valley also devel€ ncüog lu, oped on one of these buried lineaments (Toprak and Go 1993b). However, since these lineaments are covered by volcanoclastic and fluvial rocks of Plio-Quaternary age (Toprak and

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€ ncüog lu, 1993b; Dirik and Go € ncüog lu, 1996), they are not active Go (Emre et al., 2011). CAVP is surrounded by many eruption centers such as poly, genetic volcanoes and monogenetic cones (i.e., Hasandag ı) with voluminous volcanic products. The youngest acErciyesdag tivity during the late Quaternary occurred in the southwestern part , Acıgo €l and Go €llüdag ) (Fig. 1b). A number of of CAVP (i.e., Hasandag previous studies reported isotopic ages of volcanic rocks at the €l Caldera region. Different techniques have been used in Acıgo earlier studies; such as radiocarbon dating of tephra layer on sedlu et al., 1998), fission track technique on obsidiments (Kuzucuog ians (Bigazzi et al., 1993; Druitt et al., 1995; Türkecan et al., 2004), 14 C and U-series geochronology on tuffs (Roberts et al., 2001) and combined U-Th and (U-Th)/He zircon dating method on tuffs and lavas (Schmitt et al., 2011). These studies have suggested the €l Caldera reoccurrence of at least 20 volcanic events at the Acıgo gion for the last 206 ka. Few radiometric dates also exist for the  volcanism. K-Ar dating on basalts (Kuzucuog lu et al., Hasandag 1998) and U-Th/He analyses of zircon crystals on pumices (Schmitt et al., 2014) indicate 4 different volcanic events at  Composite Volcano for the last 33 ka (Table 1). Hasandag 3. Sampling material and analytical techniques Carbonate veins with thicknesses of a few mm to several cm have been precipitated parallel to the fissure walls from waters circulated through the fracture systems. Sample collection is focused on relatively thick detritus-free, moderately crystalline, banded travertine (carbonate vein). In the study area, 7 locations were found suitable for detailed sampling (locations 1, 2, 3, 4, 5, 6 and 7). The distance between the sampled locations is around a few to several hundred meters. Among all, location 4 is the outermost, which is situated nearly 750 m west of locations 1 and 2 (Fig. 2). In the study area, 36 pure carbonate samples were collected

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from 11 fracture veins (namely 1a, 1b, 2a, 2b, 2k, 3a, 3b, 4, 5, 6, 7) at 7 different locations. We dated 29 samples from these localities. However, on the basis of our field observations, only 26 samples (from locations 2a, 2b, 3a, 3b and 6) were selected for trace element, and stable (C and O) and radiogenic (Sr) isotope analyses to investigate various fluid migration pathways within differently oriented vein systems. In addition, one bed rock sample was taken from the Selime Tuff unit from location 2 (Fig. 2). Sampling was done systematically from banded travertines along both sides of the main fracture. Coordinates of the sampling sites were recorded with GPS and core and rims were marked on samples. Before the analyses, samples were cut in prismatic forms of 2e3 cm in length. U-series dating was conducted on a Nu Plasma HR Multicollector Inductively Coupled Plasma Mass Spectrometer (MCICP-MS) in the Radiogenic Isotope Laboratory at the University of Queensland (Australia) following the analytical procedures out_ lined in Zhao et al. (2001) and most recently in Ünal-Imer et al. (2016). Sr isotopic ratios were measured on the same MC-ICP-MS at the Radiogenic Isotope Laboratory of the University of Queensland. Sr isotope ratios were corrected for mass discrimination using the ratio of 86Sr/88Sr ¼ 0.1194. Long-term repeated analyses of the SRM 987 international standard yielded a mean 87Sr/88Sr value of 0.710249 ± 0.000020 (2s). The trace element analyses of the carbonate samples were performed on a Thermo X-series ICP-MS (Radiogenic Isotope Laboratory, the University of Queensland) in high performance mode with instrument conditions as described in Lawrence and Kamber (2006), after dissolving the carbonates in a 2% HNO3 solution embed with internal standards. The raw data was corrected for the low, detectable blank, internal and external drift, and for oxides and doubly charged species. Instrument response was calibrated against two independent digests of the USGS reference W-2, and confirmed by analysis of other inter-lab references, treated as

Table 1 Volcanic events dated in the last 200 ka around the study area. Eruption date (ka BP) Eruption center 4.4 ± 0.2 5.5 8.2 8.9 ± 0.6 9.8 14 16 19 20 ± 6 20.3 ± 0.6 22.3 ± 1.1 23.2 ± 3 23.8 ± 0.9 24.9 ± 0.9 25.9 ± 0.6 26 ± 1.5 28.9 ± 1.5 29 ± 1 32 ± 3 33 ± 2 75 93 ± 2 110 ± 40 117 ± 4 147 ± 8 163 ± 7 180 190 ± 9 190 ± 11 206 ± 17

€ l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo  (Aksaray) Hasandag € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo  (Aksaray) Hasandag  (Aksaray) Hasandag € l (Nevs¸ehir) Acıgo  (Aksaray) Hasandag € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo € l (Nevs¸ehir) Acıgo

Evidence

Source

€l maar, Tephra layer T17 (radiocarbon) sediment cores in the late Pleistocene Eski Acıgo €l maar, Tephra layer T15 (radiocarbon) sediment cores in the late Pleistocene Eski Acıgo €l maar, Tephra layer T13 (radiocarbon) sediment cores in the late Pleistocene Eski Acıgo  (U-Th/He method measured on zircon crystals) pumices collected from the summit of Big Hasandag €l maar, Tephra layer T10 (radiocarbon) sediment cores in the late Pleistocene Eski Acıgo €l maar, Tephra layer (radiocarbon) sediment cores in the late Pleistocene Eski Acıgo € l maar (U-Th) Acıgo acidic tephric layer with sphene and zircon (radiocarbon) Guneydag dome (fission track age) € l maar, obsidian clast nearly aphyric (U-Th/He) Acıgo Karnıyarık, rhyolitic lava nearly aphyric (U-Th/He) Kaleci, rhyolitic lava nearly aphyric (U-Th/He) , rhyolitic lava nearly aphyric (U-Th/He) Güneydag , rhyolitic lava nearly aphyric (U-Th/He) Korudag €y, rhyolitic lava nearly aphyric (U-Th/He) Tepeko Kuzey, rhyolitic lava nearly aphyric (U-Th/He) pumices collected from the flank of the volcano (U-Th/He method measured on zircon crystals) from the summit (K-Ar)  (K-Ar) south of Kocadag from the summit (K-Ar) Tas¸kesik Tepe lava dome azko € y (obsidian) Bog €l tuff (ITPFT isothermal plateau fission track age) upper Acıgo Alacasar, rhyolitic pumice aphyric (U-Th/He) Tas¸kesik, rhyolitic lava nearly aphyric (U-Th/He) €l tuffs Bog azko €y, rhyolitic pumice aphyric (U-Th/He) upper Acıgo € l tuffs (ITPFT isothermal plateau fission track) lower Acıgo azko € y, rhyolitic lava nearly aphyric (U-Th/He) Bog , rhyolitic lava weakly porphyritic (U-Th/He) Kocadag € l tuffs SW Ürgüp, rhyolitic pumice aphyric (U-Th/He) lower Acıgo

lu et al., 1998 Kuzucuog lu et al., 1998 Kuzucuog lu et al., 1998 Kuzucuog Schmitt et al., 2014 lu et al., 1998 Kuzucuog lu et al., 1998 Kuzucuog Roberts et al., 2001 lu et al., 1998 Kuzucuog Bigazzi et al., 1993 Schmitt et al., 2011 Schmitt et al., 2011 Schmitt et al., 2011 Schmitt et al., 2011 Schmitt et al., 2011 Schmitt et al., 2011 Schmitt et al., 2011 Schmitt et al., 2014 lu et al., 1998 Kuzucuog Türkecan et al., 2004 lu et al., 1998 Kuzucuog Bigazzi et al., 1993 Türkecan et al., 2004 Druitt et al., 1995 Schmitt et al., 2011 Schmitt et al., 2011 Schmitt et al., 2011 Druitt et al., 1995 Schmitt et al., 2011 Schmitt et al., 2011 Schmitt et al., 2011

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Fig. 2. Satellite image of the study area (taken from GoogleEarth) and sampling locations. Blue lines show the carbonate veins; red lines show the fractures without carbonate filling. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

unknowns. Corrections were applied for oxides using formation rates determined from pure single element REE standards. Oxygen (d18O) and carbon (d13C) stable isotope analyses of the carbonate samples were carried out at the Environmental Isotope Laboratory of the University of Arizona (USA). d18O and d13C ratios of carbonates were measured using an automated carbonate preparation device (KIEL-III) coupled to a gas-ratio mass spectrometer (Finnigan MAT 252). Powdered samples were reacted with dehydrated phosphoric acid (H3PO4) under vacuum at 70  C. The isotope ratio measurement is calibrated based on repeated measurements of international standards NBS-19 and NBS-18 and analytical precision is ±0.1‰ for d18O and ±0.08‰ for d13C (1s).

platform consists of four units: (1) Karakaya Formation, which represents the Upper Miocene fluvial and lacustrine tuff and tuffite deposits (Beekman, 1966; Ayhan and Papak, 1998); (2) pink-colored Neogene Selime Tuffs; (3) red-colored Lower Pliocene Kızılkaya  Ashes Ignimbrite (Beekman, 1966; Batum, 1978); and (4) Hasandag interbedded with lacustrine deposits (Beekman, 1966). Fig. 2 shows the distribution of faults, fissures and interested veins in the study area. Comparison of the structural data collected from different rock units enabled us to draw pattern of the crustal deformation in the region.

4. Field data

Fissures are the most common structures related to regional deformation in the study area. A large number of fissure sets are observed in various parts of the area. These are concentrated in different directions and present geometrical similarities among themselves. In the rose diagrams, fissure sets are grouped with respect to their host lithology and as to whether the fissures are filled (see Supporting data 1). By the assessment of satellite image analysis (i.e. Supporting data 2), field observations and fissure/vein rose diagrams, the fissures can be grouped in two main sets: in the range of 340 e020 (NNW&N-S and NNE sets) and in the range of 050 e100 (NE and

4.1. Outline In the study area, widespread travertine deposits cover two stratigraphic units. The unit first is the basement Paleozoic-aged  Formation, which is composed of intensely fractured Bozçaldag marble, gneiss and quartzite (Seymen, 1981; Ayhan and Papak, €çmez and Güzel, 1994). The overlying unit is the Mio1998; Go Pliocene volcanoclastic platform with horizontal and vertical facies variations of different volcanic phases (Beekman, 1966). This

4.2. Fissures

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ENE&E-W sets). NNW and N-S sets: These fissures trending in two main directions seem together (i.e. Supporting data 1a, c). They are generally occur in the southern part of the area and are mostly exposed vertically, but in some cases, having an eastern dip with about 70 . The maximum length of a fissure is up to a few tens of meters and width is a few tens of cm. There are also abundant carbonate veins as fissure-fillings observed within Selime Tuffs in the region. NNE set: Although it is not very common in the northern part of the study area, this set is observed in various areas as discontinuous fracture sets (i.e. Supporting data 1a, c, d).  formation in NE set: This set is observed close to the Bozçaldag southwestern part of the area (i.e. Supporting data 1b, d). The maximum length of fissures is up to several tens of meters. In some areas where fissures occur sequentially, they reach up to 1 km in length. Fissure widths vary from a few cm to 6 m. This set contains carbonate fillings. ENE and E-W sets: These fissures extending in two main directions in the northeastern part of the study area generally coexist (i.e. Supporting data 1c). They are rarely accompanied by WNW-trending fissures. Although they commonly occur vertically, in some cases, they dip northward with about 50 e80 . The

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maximum length of a fissure is up to a few hundred meters, while the width varies from a few cm to ten cm. They do not have any carbonate veins. Fissures in other orientations: Some fissures do not provide a systematic orientation (i.e. Supporting data 1b). These verticallyaligned fissures are generally recognized in the Kızılkaya Ignim formation. Their widths do not exceed a few brites and Bozçaldag cm and they do not contain any carbonate fillings. Faults: Evidence for faulting is observed within a limited area in the south of Yaprakhisar village (Supporting data 3a). In this area, volcanoclastic sediments are inclined northward with 05 -10 and are cut by vertical fault fractures (Supporting data 3b). Detailed observations on cutting/displacement relationship in the inclined units refer to a right lateral shear zone in a limited area (Supporting data 3c). The shear zone is extended on a fractured jog area, which is linked with well-developed open fissure set. These fissures do not have any carbonate veins. 4.3. Veins Most of fissures in the study area have been filled with carbonate. For example, in the southwestern part of the area, warm spring waters have been circulating through the deeply penetrating

Fig. 3. a. A view from a fissure-ridge travertine with a well-protected morphology over the volcanoclastics of the study area (location 1). b. An ideal main central fissure filled with carbonate vein in the area. Note that vertical compact travertine bands form symmetrical from the center of fissure.

Fig. 4. An ideal well-developed and widely-open fissure filled by incohesive cataclastic breccias in the study area.

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Fig. 5. a. The U-series ages distribution of carbonate veins with respect to fissure set orientation (strike). Note that some fissure sets activated simultaneously. b. Relative probability plot (red curve) and histogram (blue boxes) of U-series ages of samples. Note that the curve peaks become sharper when the age errors (±2s) are smaller. The histogram shows the number of ages in ka BP. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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fissures and precipitating fissure-ridge travertines over the volcanoclastics. These travertines, with a well-protected morphology, consist of a main central fissure filled with carbonate vein (vertically banded compact travertines), and porous bedded travertines dipping away from the central fissures (Fig. 3). Veins developed in the central fissures provide important data on the regional deformation. In areas where overlying bedded travertines are eroded easily, fissure veins are exposed on the bedrock. Widths of the veins are between 1 and 2 cm and 6 m. There is no opening along the central fissures (Supporting data 4).  formation at northeastern part, In remote parts of the Bozçaldag fissures have not experienced any carbonate deposition but instead they display significant open-fissure features. There are no displacements along the strike/dip of the fractures, showing only an opening, and no slickenlines on the planes of fractures. In some well-developed and widely-open fissures, incohesive cataclastic breccias filled the fractures (Fig. 4). The pressure generated by

Table 2 Geochronologic, stable (‰), and radiogenic isotope data.

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sudden changes in fluid flow during deformation has likely led to fracturing and subsequent breccia infill through the fracture. 5. Geochemical data 5.1. U-series geochronology We dated 36 samples from 7 locations around the Ihlara region (Supporting data 4a-g and 5). Fig. 5a shows the age distribution of the carbonate veins with respect to the main sets. The distribution indicates that fracture development and associated carbonate vein deposition occurred at 7 different periods in the last 150 ka (Table 2, Fig. 5a). These periods represent simultaneous activation and/or deposition of veins (Fig. 5). The distributions of U-series ages (Table 2, Fig. 5a) are summarized using probability density functions (pdf), which incorporate the 2-sigma range of each date (Fig. 5b). When compared

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simultaneous activation of the main sets in 7 different periods, we observe a tendency for peaks on the probability curves to correlate with the periods of crustal deformation (intensified crustal deformation at about 4.7, 34, 44, 53, 83, 91, 149 ka BP). Table 2 summarizes the results of the analysis of fissure development with respect to U-series ages of central and marginal parts of carbonate veins from various locations (Supporting data 4a-g). It is deduced from the age data that fissure development and thus active periods of crustal stress, except for the locations 2b and 3a, ceased within a few thousands of years. Fissures were continuously formed during active crustal deformation. Some of the fractures were activated during different stress periods. For example, fissure development dated at about 8 ka at location 2b probably records two separate events within this time interval. As shown in Fig. 5, there are two different events which occurred during this period (81.4 and 90.2 ka; Table 2, Supporting data 4b). Likewise, the prolonged activity recorded at location 3a is likely to correspond to at least 3 separate events (34, 44 and 53 ka; Table 2, Supporting data 4c).

3b-2). As characteristic for most crustal rocks, Eu displays a negative anomaly. Some of the samples are represented by slight negative Ce and strong positive Y anomalies (Fig. 6a). Carbonate veins from location 6 have the highest REE contents e nearly over four orders of magnitude greater than from other locations (Table 3). The majority of carbonates from location 2 (blue curves in Fig. 6a) displays the lowest normalized values among all samples, clustering at the bottom of the diagram (Fig. 6a). It is also noticeable that the REE compositions of samples from locations 3 & 6 (red curves in Fig. 6), except for a slight enrichment in HREEs for samples of location 6, are almost identical to those of the host rock tuff sample (Fig. 6a). This indicates that the carbonates formed in location 6 inherited their REE features mainly from the parent tuff. In addition, red-coded samples from locations 3 & 6 have distinctively low La/Gd ratios which are moderately correlated with total REEs, while blue-coded samples (location 2) show no relation with relatively smaller contents of SREE and higher La/Gd ratios (Fig. 6b). 5.3. Stable (O and C) isotope data

5.2. Trace element concentrations Rare earth element concentrations of carbonate veins samples from locations 2, 3 and 6 together with one sample from the Selime Tuff (basement rock) are shown in Table 3. Total REE contents of the samples from locations 2, 3 and 6 vary over a wide range from 19 to 13500 ppb (mean value is 1490 ppb), from 635 to 6180 ppb (mean 1930 ppb) and from 8168 to 21300 ppb (mean 12200 ppb), respectively. Since our analysis on fissures and veins in the study area revealed two main set orientations (340 e020 for locations 2a & 2b, and 050 to 100 for locations 3 & 6), in geochemical (REE, stable and radiogenic isotope) diagrams we used two different colors for these sampling localities. In a chondrite-normalized abundance diagram (Sun and McDonough, 1989) (Fig. 6a), samples show nearly flat patterns with a slight enrichment in LREEs (except for samples from location 3; e.g. 3a-1, 3a-2, 3a-5, 3b-1, and

d18O and d13C values of the whole sample set, except for the tuff sample (d13C: 12.69, d18O: 27.27‰ VSMOW), vary from 15.57 to 18.21‰ (VSMOW) and 7.64e9.31‰ (VPDB), respectively (Table 2). They have crude positive relationships in Fig. 7a. Similar to the REE systematics, stable isotope ratios of the samples from location 2 and locations 3 & 6 differentiate broadly into two groups; for instance, d13C averages at around 8.11‰ (VPDB) for samples from location 2, while it varies at around 8.41‰ (VPDB) for the other group (locations 3 & 6). These isotopically-enriched d13C values are comparable with modern d13C values of the geothermal waters around the study area such as in the Ziga geothermal field, located at about 1 km NE of the studied veins. Geothermal waters have a d13C ratio of 6.7‰ (VPDB) (Afs¸in et al., 2014), which is close to the d13C range (7.64e9.31‰) of the studied carbonate veins. Also d18O ratios of the geothermal waters around Ziga, Yaprakhisar and Acigol (Fig. 1) vary

Table 3 Trace element concentrations of the studied carbonate veins and Selime Tuff (ppb); Sr concentrations are in ppm. Sample

La

Ce

Pr

Nd

Sm

Eu

Gd

Tb

Dy

Y

Ho

Er

Tm

Yb

Lu

Sr

Y/Ho

2k-1 2k-2 2a-1 2a-2 2a-3 2a-4 2b-1 2b-2 2b-3 2b-4 2b-5 2b-6 2b-7 3a-1 3a-2 3a-3 3a-4 3a-5 3b-1 3b-2 6e1 6e2 6e3 6e4 6e5 6e6

68.5 113.1 8.7 6.5 3.1 19.8 207.3 8.2 93.6 2798.3 26.4 440.1 10.2 39.7 44.1 285.2 69.9 61.1 237.2 26.2 1141.8 1342.4 1297.0 2639.2 1777.4 861.0

161.7 281.0 9.5 10.1 5.4 31.6 346.6 12.3 134.4 4261.1 37.6 677.0 11.6 61.1 57.0 445.1 137.3 77.2 322.1 34.5 1671.4 2042.5 1878.3 3831.6 2560.4 1190.1

11.5 20.4 1.2 1.4 0.6 3.4 33.0 1.4 16.7 421.6 4.3 73.2 1.3 8.9 10.0 62.1 14.6 13.4 58.0 5.9 171.3 207.9 201.3 409.2 271.0 134.5

37.8 72.5 5.1 6.9 2.0 12.0 102.4 3.6 50.9 1379.6 17.8 275.8 4.3 38.2 51.6 247.7 55.6 58.0 296.9 25.9 614.6 751.0 741.9 1511.9 1004.7 513.0

6.6 11.8 0.8 1.0 0.4 2.7 16.4 0.8 8.9 262.1 3.7 65.2 0.9 10.8 15.3 59.6 13.0 13.4 98.7 7.7 134.0 159.8 166.0 335.1 218.9 124.6

1.3 2.2 0.2 0.4 0.0 0.5 2.7 0.4 1.5 37.5 1.1 17.9 0.0 3.8 6.5 20.4 4.3 5.0 41.6 3.6 31.5 36.4 42.2 81.3 53.4 34.0

6.3 11.3 1.1 1.4 0.4 1.9 13.8 0.8 8.1 288.8 4.9 98.6 0.6 22.1 36.0 101.9 22.8 25.3 214.8 18.7 213.0 252.5 284.7 549.4 363.0 221.9

1.1 1.5 0.2 0.4 0.0 0.4 2.0 0.1 1.3 51.9 0.9 18.7 0.1 4.2 7.0 19.1 4.3 4.8 42.4 3.9 41.0 48.5 53.4 105.7 68.8 43.2

5.8 9.1 0.9 2.3 0.2 2.5 11.8 0.6 7.1 365.8 6.1 135.3 0.6 30.4 58.6 141.8 30.2 40.7 331.7 29.9 322.5 364.4 402.0 804.9 533.3 322.6

31.7 42.5 15.5 21.0 6.3 19.5 65.6 11.1 38.3 2804.3 50.7 1261.1 8.0 352.3 780.6 1581.5 392.0 411.9 3825.1 407.5 3671.1 3957.3 4694.0 9112.5 6159.0 3931.7

1.0 1.7 0.3 0.4 0.1 0.4 2.8 0.2 1.2 87.1 1.3 32.7 0.1 7.6 15.4 35.6 8.1 9.7 83.2 8.3 84.3 93.9 107.0 210.4 139.1 85.1

3.3 5.0 0.7 1.5 0.2 1.1 6.5 0.7 3.3 275.9 3.8 98.5 0.4 24.6 52.6 111.4 26.8 28.6 267.1 27.6 278.2 315.3 352.3 687.0 460.8 284.9

0.4 0.7 0.1 0.3 0.0 0.2 1.0 0.1 0.6 45.8 0.6 15.6 0.0 3.7 8.0 16.9 4.4 4.6 40.1 4.2 46.1 51.2 56.8 112.5 76.2 46.1

3.1 5.1 1.2 1.7 0.2 1.6 5.5 0.7 3.8 344.1 3.7 109.3 0.2 26.5 58.9 115.5 27.9 29.5 276.0 27.4 335.6 365.2 404.0 801.8 535.7 325.0

0.5 0.8 0.1 0.2 0.0 0.2 0.7 0.1 0.5 52.8 0.7 15.9 0.0 4.1 8.5 17.1 4.8 4.5 40.3 4.2 53.2 58.0 63.0 126.1 84.4 50.0

987 950 1096 768 1017 886 878 1045 936 982 997 824 1129 848 867 963 1028 703 946 883 708 653 659 656 655 699

30.7 25.7 57.1 57.3 74.1 47.3 23.7 66.8 31.3 32.2 38.9 38.5 75.3 46.3 50.6 44.5 48.1 42.4 46.0 49.0 43.5 42.2 43.9 43.3 44.3 46.2

Tuff

4089.5

4630.6

700.2

2248.9

422.6

57.6

363.4

54.4

298.8

1548.9

56.4

141.1

20.3

125.4

16.7

987

27.5

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167

Fig. 6. a. Chondrite-normalized (Sun and McDonough, 1989) rare earths and yttrium (REY) patterns of carbonate veins and host tuff material from the study area. b. La/Gd versus SREE (ppb) for all analyzed vein carbonates from Ihlara region. Samples have been separated into distinct geochemical groups: samples from locations 3 & 6 are denoted by red data points, while samples of location 2 are shown by blue data points. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

between 9.41 and 12.6‰ VSMOW (Burcak, 2009), which are substantially lower than that of the carbonate veins from the study area (15.57e18.21‰). 5.4. Sr isotope data 87 Sr/86Sr values of samples vary in a narrow range from 0.709338 ± 0.000010 to 0.710023 ± 0.000009 (Table 2). These values are slightly higher than those of modern seawater (average: 0.7092; Veizer, 1989) (Fig. 7b) and Cenozoic seawater (0.7080e0.7090; Capo et al., 1998). The range of Sr isotope values of the carbonate veins plots in the Sr isotope range of the Late € ksal and Cretaceous - Early Tertiary Central Anatolian plutons (Ko € ncüoglu, 2008), while it displays much higher values than Go those of the Upper Miocene Cappadocian ignimbrites and lavas (Temel et al., 1998) and the Bilecik limestones (Akıllı and Mutlu, 2016) and dolomites of Bolkar carbonate platform (Kırmacı, 2013) in close proximity (to the south) to the study area. There is a moderate correlation between Sr isotope composition and Sr (ppm) concentrations of the samples (Fig. 7c); as Sr content increases, 87Sr/86Sr value decreases, becoming less radiogenic. It is

interesting that younger (~35e55 ka BP) carbonate veins from locations 3 & 6 (the samples denoted by red data points, Fig. 7b and c) are represented by more radiogenic Sr than the older (~75e90 ka BP) veins from location 2 (with blue data points, Fig. 7b and c), implying two different or modified fluid sources responsible for the deposition of veins. Indeed, 87Sr/86Sr values range from 0.709338 to 0.709502 (average: 0.709411) among the samples from location 2 (Table 2), whereas they yield a range of 0.709683e0.710023 (average: 0.709929) for other locations. Further, these isotopically distinct two populations show positive and negative correlations with d13C values, respectively (Fig. 7d) as well as distinctively different populations when plotted vs. Y/Ho and La/Gd (Fig. 7eef). 6. Discussion 6.1. Implication of U-series age data for crustal deformation and strain cycles in the CAVP 6.1.1. Regional tectonics Our detailed field analysis and bi-directional rose diagrams plotted for fissures and veins in the study area reveal two dominant

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Fig. 7. a. d 18O vs. d 13C systematics for carbonate veins, b. 87Sr/86Sr ratios of the studied carbonate veins, according to their U-series ages (Table 2) and regional Sr isotope data of the € ksal and Go € ncüoglu, 2008; Akıllı and Mutlu, 2016), c. 87Sr/86Sr vs. Sr (ppm), d. 87Sr/86Sr versus d13C plots of the carbonate samples. Note that red bedrock (Temel et al., 1998; Ko circles show the data of samples from locations 3 & 6, while blue circles denote for the samples of location 2, e. Y/Ho vs. 87Sr/86Sr, f. La/Gd vs. 87Sr/86Sr. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

stress orientations in a range of 340 e100 . In this frame, some fissure sets occur in the range of 340 e020 (NNW&N-S and NNE sets), while some others vary from 050 to 100 (NE and ENE&E-W sets). There are two plausible interpretations regarding the tectonic origin of these two subgroups: They are controlled by (1) tri-axial (double conjugated 4 sets; NNW&N-S, NNE, NE, ENE&E-W) or (2) uniaxial (size of intermediate and smallest principle stress are the same) stress. All fissures represent notable opening fissure features (Mode I extension fractures). There are no slickenlines on their planes. Single faulting evidence is observed within a right-lateral shear zone in a limited linking area of two well-developed opening

fissures set (Supporting data 3). As commonly expected along the opening fractures around a magmatic intrusion, strike-slip faults may develop at the tip of them and the opening fractures could be connected to each other by shear zones (Hill, 1977; Rubin and Gillard, 1998). In the study area, there is no evidence for compressional tectonic. All units in the Pliocene volcanoclastic platform maintain their horizontal position. Consequently, it is quite plausible that such fractures were formed under the influence of tensile stress normal to the dominant orientations (in a range of 340 e100 ). The intraplate crustal deformation in Central Anatolia is associated with the compression related to convergence of the Afro-

V. Karabacak et al. / Quaternary Science Reviews 177 (2017) 158e172

Arabian continent toward north and/or the extension due to southward rollback of the African subduction under Aegean€r et al., 1985; Dhont et al., 1998). However, our Anatolia (i.e. S¸engo results are in favor of extension with the influence of a NW-SE striking tension stress, which is consistent with the recent GPS  et al., 2013; Simao studies in Central Anatolian region (e.g. Aktug et al., 2016). 6.1.2. Strain cycles of crustal deformation Fig. 5a displays the age distribution of carbonate veins with respect to fissure sets. In this distribution, it could be concluded that two independent fracture systems work in sequence. NNEtrending first fracture group (in the range of 340 e020 ) has carbonate veins with older ages (except for the age 4.7 ka). Carbonate precipitation along these fractures occurred simultaneously in a period between 83, 91 and 149 ka BP. On the other hand, the ENEtrending group (in the range of 050 e100 ) contains carbonate veins with younger ages. The simultaneous carbonate deposition in these fractures took place in a period from 34, 44 to 53 ka BP. The youngest age (4.7 ka BP) shows that the first group of fractures goes back to the activity. This is supported by the fact that the existing hot water spots (e.g. Ziga hot water) are aligned along the fractures of the first group. The age data for carbonate veins indicate that the crustal deformation intensified during 7 different periods at about 4.7, 34, 44, 53, 83, 91 and 149 ka BP (Fig. 5). At least four of these periods (4.7, 34, 91 and 149 ka BP) correspond to the onset of cycles of volcanic activity in this region reported in the previous studies € l caldera (Table 4). For example, the volcanic eruptions in the Acıgo region dated at 4.4 ± 0.2, 32 ± 3, 93 ± 2 and 147 ± 8 ka BP lu et al., 1998; Türkecan et al., 2004; Schmitt et al., 2011) (Kuzucuog  and another eruption occurred at 33 ± 2 ka BP on the Hasandag lu et al., 1998). There has been no composite Volcano (Kuzucuog record of volcanic eruptions for ages of 44, 53, and 83 ka BP. There are two plausible interpretations of this phenomenon: (1) It is possible that there is a lack of dating on volcanic eruption products around study area. There could also be unrecorded and unpreserved volcanoclastic layers due to depositional and erosional lu et al., 1998) or heating events resetting processes (e.g., Kuzucuog isotopic age of extrusive materials (e.g., Blondes et al., 2007; Schmitt et al., 2011), rendering the identification of eruption products difficult. (2) In some cases, however, deformation could have been caused by strain cycles of magmato-tectonic events without any surface extrusion (Rubin and Gillard, 1998; Rubin, 1992; Azzaro, 1999; Gudmundsson, 2003; Zobin, 2003; Gudmundsson and Loetveit, 2005; Doubre et al., 2007; Doubre and Peltzer, 2007; Medynski et al., 2015; Dumuont et al., 2017). The deformation cycles may be attributed to sub-volcanic magma movements and/or associated fluid pressure, which can be responsible for some surface ruptures at the tip of magma body.

169

6.1.3. Dilatation rate U/Th dating results of carbonate veins indicate that fracture systems did not open during a single deformation event, but rather developed as an accumulation of several periodic deformation events. Sampling from centers to the both margins of fissure veins on location 2 and 3 provides information on the dilatation rate during the strain cycles. Veins 2a and 2b at the location 2 have similar strike (first group of fissures in the range of 340 e020 ). Location 3 includes the second group of fissures (in the range of 050 to 100 ). Supporting data 6 show the age results of sampling along the carbonate veins from 2a, 2b and 3a fissures. Considering the relationship between the age results and distance from the fissure wall, it can be concluded that individual fissures have been dilating and veins have been depositing at average rates between 0.01 and 0.0131 mm yr1 during the strain cycles. In a previous study (Altunel and Karabacak, 2005) at the Pamukkale travertine site of Western Turkey, which is one of the most actively extending regions in the world, dilatation rates of individual fissures were estimated in the range of 0.001e0.1 mm yr1. When compared with the data of Altunel and Karabacak (2005), although every fracture has not been dated in the study area, the rate of dilatation/deposition in the study area is very high. 6.2. Fluid source and implication on the magmato-tectonic origin of CO2 degassing 6.2.1. Stable (O & C) isotopes Notably high carbon and oxygen isotope values of samples indicate no organic input but rather show a significant effect of decarbonization reactions, resulted in CO2 degassing. Releasing of light-isotopes (16O and 12C) from carbon dioxide gave rise to residual fluid to be enriched in heavy isotopes. Precipitation from such isotopically-enriched fluids well explains the isotopically heavy character of the studied carbonate veins (e.g., Uysal et al., € 2007; Ozkul et al., 2014). d18O values of Ziga and Yaprakhisar geothermal waters range from 10.6 to 11.5‰ (VSMOW) (Burcak, 2009; Afs¸in et al., 2014). Using the oxygen isotope fractionation between calcite and water (D18OCalcite-Water) (Friedman and O'Neil, 1977), a d18Owater value of fluids equilibrating with carbonate veins was computed in the range of 11.8 to 9.17‰ (average: 11.1‰) for 30  C and 9.9 to 7.3‰ (average: 9.2‰) for 40  C, which clearly indicate a meteoric origin. Assuming that discharge temperatures of Ziga and Yaprakhisar have not significantly changed in the studied time interval, estimated d18Owater values are quite consistent with those given by Afs¸in et al. (2014) and Burcak (2009). Previous studies (e.g., Ercan et al., 1995; Gulec et al., 2002) around the study area indicated notable amounts of mantle-He (almost ~ 35% of the total helium inventory) and high CO2 concentrations in the thermal fluids (Mutlu et al., in prep.). There is no

Table 4 Comparison between the crustal deformation events investigated in the study area and the volcanic eruption events in the surrounding region from the literature. Note that the crustal deformation periods and uncertainties are calculated from probability density functions in Fig. 5b. Crustal deformation (ka BP)

Fissure set

Volcanic eruption (ka BP)

4.7 ± 0.15 34 ± 1

340 e20 50 e100

€l Acıgo  (Acıgo € l) Kocadag  Hasandag

lu et al., 1998 Kuzucuog Türkecan et al., 2004 lu et al., 1998 Kuzucuog

44 ± 0.6 53 ± 3.5 83 ± 2.5 91 ± 1.5 149 ± 2.5

50 e100 50 e100 340 e20 340 e20 340 e20

4.4 ± 0.2 32 ± 3 33 ± 2

93 ± 2 147 ± 8

azko € y (Acıgo €l) Bog €l) Tas¸kesik (Acıgo

Türkecan et al., 2004 Schmitt et al., 2011

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doubt that volcanism is the chief mechanism contributing to the volatile inventory of the Central Anatolian fluids. However, d13C (CO2) values of fumaroles in the region are mostly within the range of marine limestone (±2‰ vs. VPDB) (Mutlu et al., in prep.). Carbon isotope compositions of studied carbonate veins (from 7.64 to 9.31‰) are considerably higher than the limestone range (Rollinson, 1993). This is probably due to carbon isotope fractionation during the precipitation, which caused CO2 degassing from the springs to have d13C values lower than the residual fluid which crystallized the carbonate veins. 6.2.2. Radiogenic Sr isotopes and trace elements Samples from location 2 (Fig. 7b) have relatively lower Sr isotope compositions than the samples from other locations (locations 3 & 6), which are closer to Sr isotope values of modern seawater (87Sr/86Sr averaging at around 0.7090 for Quaternary and lower for Cenozoic: Veizer, 1989; McArthur et al., 2012). However, the input of the modern seawater or limestones can obviously be excluded in this area. These two geochemically distinctive groups are readily identified in both Figs. 6 and 7, suggesting at least two diverse non-marine fluid sources. The difference in Sr isotope values between carbonates from locations 3 & 6 and location 2 can be attributed to different water-rock interaction history. Lower 87 Sr/86Sr of samples at location 2 may be due to mixing of fluids that interacted with both lava and tuff units with much lower Sr isotope values and plutons with more radiogenic isotope compositions (Fig. 7b). Sr isotope data of samples at locations 3 & 6 samples indicate however, interaction of meteoric fluids mainly with plutons without a full contact with tuff units. This would imply that the circulation within open fractures exceeded >100 m through the Pliocene volcanoclastic cover. Conformingly, in a87Sr/86Sr vs. 1/Sr (ppm) plot (Fig. 7c), samples from location 2 illustrate a linear two-component mixing line suggesting that the fluids from which the carbonates at this location precipitated consisted of two end members. Samples from locations 3 & 6 exhibit, however, no mixing line indicating no significant fluid mixing for these samples. Chondrite-normalized REE diagrams of the carbonate veins (Fig. 6a) may be interpreted as indicating some additional marine sources, where the majority of the vein samples displays positive Y anomalies and some show slight negative Ce anomalies (Bau et al., 1997). Positive Y anomalies of carbonates, however, may also have resulted from fluorite-rich deeply-circulated aqueous fluids (Loges et al., 2013; Bau and Dulski, 1996), where Y shows distinct fractionation specifically against geochemically similar Ho. Also negative Ce anomalies (not distinct and not observed in all samples) may indicate oxidising environments of the carbonate precipitation. 7. Conclusions We provide direct field evidence of recent stress directions and investigate carbonate-filled fracture systems by U/Th geochronology and isotope geochemistry to evaluate the episodes of latest volcanic activity under regional stress in the Central Anatolian Volcanic Province: 1. Two independent fracture systems are in favor of extension with the influence of a NW-SE striking tension stress in the southern Central Anatolian Volcanic Province. Successive fracture development in the region has been controlled by two different  Composite Volcano and volcanic eruption centers (Hasandag €l Caldera). Acıgo 2. Trace element, and stable (C and O) and radiogenic (Sr) isotope compositions of carbonate veins indicate different fluid migration pathways for two different fracture systems.

3. U/Th age data for carbonate veins of two independent fracture systems indicate that the crustal deformation intensified during 7 episodic periods in the last 150 ka. The results show that there is high rate of dilatation in the region. 4. The NNE-trending fracture system was formed as a result of strain cycles in a period from 149 ± 2.5, 91 ± 1.5 to 83 ± 2.5 ka BP. Subsequent deformation events represented by the ENEtrending second fracture zone have been triggered during the period of 53 ± 3.5, 44 ± 0.6 to 34 ± 1 ka BP, before the first (NNEtrending) fracture zone resumed the activity at about 4.7 ± 0.15 ka BP. 5. U/Th ages of carbonates precipitated in volcanically active regions may be useful to determine recurrence intervals of volcanic activities. However, further studies are needed to evaluate statistical correlations between the precise ages of carbonates and of volcanic rocks. Acknowledgements This study has been funded by the Scientific and Technological _ Research Council of Turkey (TÜBITAK) with the project no. 115Y497. Stable (C and O) isotope analysis of samples was funded by the Eskisehir Osmangazi University Research Foundation (project no: 2016-1007). Authors appreciate the supportive comments of Axel K. Schmitt and one anonymous reviewer, which greatly improved the manuscript. Appendix A. Supplementary data Supplementary data related to this article can be found at https://doi.org/10.1016/j.quascirev.2017.10.022. References € 2014. Mixing Afs¸in, M., Allen, D.M., Kirste, D., Durukan, U.G., Gurel, A., Oruc, O., processes in hydrothermal spring systems and implications for interpreting geochemical data: a case study in the Cappadocia region of Turkey. Hydrogeology J. 22, 7e23. https://doi.org/10.1007/s10040-013-1056-2. Akıllı, H., Mutlu, H., 2016. Chemical and stable-radiogenic isotope compositions of Polatlı-Haymana thermal waters (Ankara, Turkey). In: EGU General Assembly 2016, pp. 18e22. April 2016, Vienna, Austria. € , B., Parmaksız, E., Kurt, M., Lenk, O., Kılıçog lu, A., Gürdal, M.A., Ozdemir, Aktug S., 2013. Deformation of Central Anatolia: GPS implications. J. Geodyn. 67, 78e96. Alessandro, W.D., Giammanco, S., Bellomo, S., Parello, F., 2007. Geochemistry and mineralogy of travertine deposits of the SW flank of Mt. Etna (Italy): relationships with past volcanic and degassing activity. J. Volcanol. Geotherm. Res. 165, 64e70. Altunel, E., Karabacak, V., 2005. 2005, Determination of horizontal extension from fissure-ridge travertines: a case study in the Denizli Basin, southwestern Turkey. Geodin. Acta 18/3-4, 333e342. Aydar, E., Gourgaud, A., Deniel, C., Lyberis, N., Gundogdu, N., 1995. Le volcanisme quaternaire d'Anatolie centrale (Turquie) : association de magmatisme calcoalcalin et alcalin en domaine de convergence. Can. J. Earth Sci. 32 (7), 1058e1069. Aydar, E., Gundogdu, N., Bayhan, H., Gourgaud, A., 1994. Volcano-structural and petrological investigation of the Cappadocian Quaternary volcanism. TUBITAK Yerbilim. Derg. 3, 25e42 (In Turkish with English abstract). Aydar, E., Schmitt, A.K., Çubukçu, H.E., Akin, L., Ersoy, O., Sen, E., Atici, G., 2012. Correlation of ignimbrites in the Central Anatolian Volcanic Province using zircon and plagioclase ages and zircon compositions. J. Volcanol. Geotherm. Res. 213, 83e97. _ 1998. Aksaray-tas¸pınar-altınhisar-çiftlik-delihebil (Nig de) CivAyhan, A., Papak, I., ü Jeoloji Etüdleri Daire Bas¸kanlıg ı, Ankara. arının Jeolojisi. MTA Genel Müdürlüg Rapor No: 2324. Azzaro, R., 1999. Earthquake surface faulting at Mount Etna volcano (Sicily) and implications for active tectonics. J. Geodyn. 28, 193e213. Batum, I., 1978. Geology and petrography of acıgol and golludag volcanics at southwest of nevs¸ehir Central Anatolia, Turkey. Yerbilimleri 41e2, 50e69 (In Turkish with English abstract). Bau, M., Dulski, P., 1996. Distribution of yttrium and rare-earth elements in the penge and kuruman iron-formations, Transvaal Supergroup, South Africa. Precambr. Res. 79, 37e55. Bau, M., Moller, P., Dulski, P., 1997. Yttrium and lanthanides in eastern Mediterranean seawater and their fractionation during redox-cycling. Mar. Chem. 56.

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